1. Field of the Invention
The present invention relates to semiconductor integrated circuit manufacturing and, more particularly, to a method of forming stress-tuned silicon nitride thin films and to a method of depositing the silicon nitride films using plasma enhanced atomic layer deposition (PEALD) at low temperature (under, e.g., 400° C.).
2. Description of the Related Art
Silicon nitride layers deposited at low temperatures (less than 400° C.) have been used in a number of important applications for memory devices, for example, as a passivation layer, a surface protection layer and/or a spacer for a transistor gate. Silicon nitride films may be formed by plasma enhanced chemical vapor deposition (PECVD) method. The main advantages of the PECVD method over other CVD methods are high deposition rates and controllability over a wide range of refractive indices. A further advantage of the PECVD method is that the process can take place at a relatively low temperature, for example temperatures under 400° C., keeping the total thermal budget of the cell processing to a minimum.
In recent years, silicon nitride layers have been used in structures which improve the carrier mobility in n-p channel MOSFET devices having different stress (some exhibiting tensile stress and some exhibiting compressive stress) as shown in U.S. 2003/0040158 A1 by Saitoh. Preferably, a silicon nitride layer which has tensile stress is formed by a low pressure CVD process, and a silicon nitride layer which has compressive stress is formed by PECVD process. According to the technology disclosed by Saitoh, in order to produce silicon nitride layers having adverse stress characteristics, entirely different deposition methods must be used.
In an embodiment, the present invention provides a method of forming stress-tuned silicon nitride thin films using plasma enhanced atomic layer deposition (PEALD) at low temperature (under, e.g., 400° C.).